Control system and method for coordinating throttle and boost

ABSTRACT

An engine control system according to the principles of the present disclosure includes a manifold air pressure (MAP) determination module, a boost control module, and a throttle control module. The MAP determination module determines a desired MAP based on a driver torque request. The boost control module controls a boost device based on the desired MAP and a basic boost pressure. The boost device is actuated using boost pressure and the boost pressure is insufficient to actuate the boost device when the boost pressure is less than the basic boost pressure. The throttle control module controls a throttle valve based on the desired MAP and the basic boost pressure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/497,691, filed on Jun. 16, 2011. The disclosure of the aboveapplication is incorporated herein by reference in its entirety.

FIELD

The present disclosure relates to engine control systems and methods,and more particularly, to control systems and methods for coordinatingthrottle and boost.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Internal combustion engines combust an air and fuel mixture withincylinders to drive pistons, which produces drive torque. Airflow intothe engine is regulated via a throttle. More specifically, the throttleadjusts throttle area, which increases or decreases airflow into theengine. As the throttle area increases, the airflow into the engineincreases. A boost device, such as a turbocharger or a supercharger, mayalso increase the airflow into the engine. A fuel control system adjuststhe rate that fuel is injected to provide a desired air/fuel mixture tothe cylinders and/or to achieve a desired torque output. Increasing theamount of air and fuel provided to the cylinders increases the torqueoutput of the engine.

In spark-ignition engines, spark initiates combustion of an air/fuelmixture provided to the cylinders. In compression-ignition engines,compression in the cylinders combusts the air/fuel mixture provided tothe cylinders. Spark timing and airflow may be the primary mechanismsfor adjusting the torque output of spark-ignition engines, while fuelflow may be the primary mechanism for adjusting the torque output ofcompression-ignition engines.

Engine control systems have been developed to control engine outputtorque to achieve a desired torque. Traditional engine control systems,however, do not control the engine output torque as accurately asdesired. Further, traditional engine control systems do not provide arapid response to control signals or coordinate engine torque controlamong various devices that affect the engine output torque.

SUMMARY

An engine control system according to the principles of the presentdisclosure includes a manifold air pressure (MAP) determination module,a boost control module, and a throttle control module. The MAPdetermination module determines a desired MAP based on a driver torquerequest. The boost control module controls a boost device based on thedesired MAP and a basic boost pressure. The boost device is actuatedusing boost pressure and the boost pressure is insufficient to actuatethe boost device when the boost pressure is less than the basic boostpressure. The throttle control module controls a throttle valve based onthe desired MAP and the basic boost pressure.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples areintended for purposes of illustration only and are not intended to limitthe scope of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of an example engine systemaccording to the principles of the present disclosure;

FIG. 2 is a functional block diagram of an example engine control systemaccording to the principles of the present disclosure;

FIG. 3 is a functional block diagram of an example engine control moduleaccording to the principles of the present disclosure;

FIG. 4 is a flowchart illustrating an example engine control methodaccording to the principles of the present disclosure;

FIG. 5 is a graph illustrating example manifold air pressure (MAP)control curves according to the principles of the present disclosure;

FIG. 6 is a graph illustrating an example boost control curve accordingto the principles of the present disclosure; and

FIG. 7 is a graph illustrating an example throttle control curveaccording to the principles of the present disclosure.

DETAILED DESCRIPTION

The following description is merely illustrative in nature and is in noway intended to limit the disclosure, its application, or uses. Forpurposes of clarity, the same reference numbers will be used in thedrawings to identify similar elements. As used herein, the phrase atleast one of A, B, and C should be construed to mean a logical (A or Bor C), using a non-exclusive logical or. It should be understood thatsteps within a method may be executed in different order withoutaltering the principles of the present disclosure.

As used herein, the term module may refer to, be part of, or include anApplication Specific Integrated Circuit (ASIC); an electronic circuit; acombinational logic circuit; a field programmable gate array (FPGA); aprocessor (shared, dedicated, or group) that executes code; othersuitable components that provide the described functionality; or acombination of some or all of the above, such as in a system-on-chip.The term module may include memory (shared, dedicated, or group) thatstores code executed by the processor.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes,and/or objects. The term shared, as used above, means that some or allcode from multiple modules may be executed using a single (shared)processor. In addition, some or all code from multiple modules may bestored by a single (shared) memory. The term group, as used above, meansthat some or all code from a single module may be executed using a groupof processors or a group of execution engines. For example, multiplecores and/or multiple threads of a processor may be considered to beexecution engines. In various implementations, execution engines may begrouped across a processor, across multiple processors, and acrossprocessors in multiple locations, such as multiple servers in a parallelprocessing arrangement. In addition, some or all code from a singlemodule may be stored using a group of memories.

The apparatuses and methods described herein may be implemented by oneor more computer programs executed by one or more processors. Thecomputer programs include processor-executable instructions that arestored on a non-transitory tangible computer readable medium. Thecomputer programs may also include stored data. Non-limiting examples ofthe non-transitory tangible computer readable medium are nonvolatilememory, magnetic storage, and optical storage.

A throttle valve may be controlled based on a desired throttle area anda boost device may be controlled based on a desired boost pressure. Thedesired throttle area and the desired boost pressure may both bedetermined based on a desired manifold air pressure (MAP). Boostpressure produced by the boost device may be controlled by opening awastegate to allow airflow to bypass the boost device entirely (e.g.,bypass a supercharger) or partially (e.g., bypass a turbine of aturbocharger).

The wastegate of the boost device may be actuated using the boostpressure. The boost pressure is insufficient to actuate the wastegatewhen the boost pressure is less than a basic boost pressure. The basicboost pressure depends on atmospheric pressure and the design of theboost device.

The response gains of the throttle valve and the boost device may beaffected by intake airflow. The response gain of the throttle valve isthe ratio of change in the flow rate through the throttle valve tochange in the throttle area of the throttle valve. The response gain ofthe boost device is the ratio of change in the boost pressure to changein an actuation percentage (i.e., a duty cycle) of the wastegate. Thewastegate may be opened and closed by respectively decreasing andincreasing the duty cycle.

The response gain of the throttle valve may be most consistent (i.e.,within a desired range) when a desired pressure ratio across thethrottle valve is less than a first ratio (e.g., 0.9). The desiredpressure ratio is the ratio of a desired pressure downstream from thethrottle valve (i.e., the desired MAP) to the pressure upstream from thethrottle valve. The pressure upstream from the throttle valve may beequal to atmospheric pressure when the boost pressure is less than thebasic boost pressure. Thus, the desired pressure ratio across thethrottle valve may be 0.9 when the desired MAP is equal to 90 percent ofthe atmospheric pressure.

The response gain of the boost device may be most consistent when theduty cycle of the wastegate is greater than a first percentage (e.g., 30percent). The duty cycle of the wastegate may be equal to the firstpercentage when the desired MAP is equal to a first pressure. The firstpressure may be approximately 10 kilopascals (kPa) greater than thebasic boost pressure.

An engine control system and method according to the present disclosurecoordinates actuation of the throttle valve and the boost device byusing the actuators to adjust intake airflow when the response gains ofthe actuators are most consistent. The throttle valve is used as aprimary actuator for adjusting the intake airflow when the desired MAPis less than the first pressure. The throttle valve may be used asprimary actuator for adjusting the intake airflow by adding a boostoffset pressure to the desired MAP and determining the desired boostpressure based on the offset desired MAP. The boost offset pressure maybe predetermined to fully close the boost device.

The boost device is used as a primary actuator for adjusting the intakeairflow when the desired MAP is greater than the first pressure. Theboost device may be used as the primary actuator for adjusting theintake airflow by adding a throttle offset pressure to the desired MAPand determining the desired throttle area based on the offset desiredMAP. The boost offset pressure may be predetermined to fully open thethrottle valve. In turn, the throttle valve may only be used to adjustthe intake airflow when the boost device overshoots the desired MAP bymore than the throttle offset pressure.

Coordinating actuation of the throttle valve and the boost device inthis manner improves the ability to control engine torque, improvesdrivability, improves boost diagnostics, reduces pumping losses, andimproves boost overshoot protection. Drivability is improved byproviding more boost than necessary at lower torque levels, causing theresponse gain of the boost device to be more consistent at lower torquelevels. As a result, the response gain of the boost device is consistentmore frequently, improving boost diagnostic methods that may only beperformed when the response gain of the boost device is consistent.

Pumping losses are reduced by opening the throttle valve more thannecessary at higher torque levels, which reduces intake airflowrestrictions and, in turbocharged engine systems, reduces exhaustbackpressure. Boost overshoot protection may be improved by graduallyclosing the throttle valve to limit an actual MAP to the desired MAPwhen the boost device overshoots the desired MAP by more than thethrottle offset pressure. The throttle valve may be reopened when theboost device can limit the actual MAP to the sum of the desired MAP andthe throttle offset pressure.

Referring now to FIG. 1, a functional block diagram of an exemplaryengine system 100 is presented. The engine system 100 includes an engine102 that combusts an air/fuel mixture to produce drive torque for avehicle based on driver input from a driver input module 104. Air isdrawn into the engine 102 through an intake system 108. For exampleonly, the intake system 108 may include an intake manifold 110 and athrottle valve 112. For example only, the throttle valve 112 may includea butterfly valve having a rotatable blade. An engine control module(ECM) 114 controls a throttle actuator module 116, which regulatesopening of the throttle valve 112 to control the amount of air drawninto the intake manifold 110.

Air from the intake manifold 110 is drawn into cylinders of the engine102. While the engine 102 may include multiple cylinders, forillustration purposes a single representative cylinder 118 is shown. Forexample only, the engine 102 may include 2, 3, 4, 5, 6, 8, 10, and/or 12cylinders. The ECM 114 may instruct a cylinder actuator module 120 toselectively deactivate some of the cylinders, which may improve fueleconomy under certain engine operating conditions.

Although the discussion below describes a four-stroke cycle, the engine102 may operate using a four-stroke cycle or a two-stroke cyle. Afour-stroke cycle includes an intake stroke, a compression stroke, acombustion stroke, and an exhaust stroke. During each revolution of acrankshaft (not shown), two of the four strokes occur within thecylinder 118. Therefore, two crankshaft revolutions are necessary forthe cylinder 118 to experience all four of the strokes.

During the intake stroke, air from the intake manifold 110 is drawn intothe cylinder 118 through an intake valve 122. The ECM 114 controls afuel actuator module 124, which regulates fuel injection to achieve adesired air/fuel ratio. Fuel may be injected into the intake manifold110 at a central location or at multiple locations, such as near theintake valve 122 of each of the cylinders. In various implementations(not shown), fuel may be injected directly into the cylinders or intomixing chambers associated with the cylinders. The fuel actuator module124 may halt injection of fuel to cylinders that are deactivated.

The injected fuel mixes with air and creates an air/fuel mixture in thecylinder 118. During the compression stroke, a piston (not shown) withinthe cylinder 118 compresses the air/fuel mixture. The engine 102 may bea compression-ignition engine, in which case compression in the cylinder118 ignites the air/fuel mixture. Alternatively, the engine 102 may be aspark-ignition engine, in which case a spark actuator module 126energizes a spark plug 128 in the cylinder 118 based on a signal fromthe ECM 114, which ignites the air/fuel mixture. The timing of the sparkmay be specified relative to the time when the piston is at its topmostposition, referred to as top dead center (TDC).

The spark actuator module 126 may be controlled by a timing signalspecifying how far before or after TDC to generate the spark. Becausepiston position is directly related to crankshaft rotation, operation ofthe spark actuator module 126 may be synchronized with crankshaft angle.In various implementations, the spark actuator module 126 may haltprovision of spark to deactivated cylinders.

Generating the spark may be referred to as a firing event. The sparkactuator module 126 may have the ability to vary the timing of the sparkfor each firing event. The spark actuator module 126 may even be capableof varying the spark timing for a next firing event when the sparktiming signal is changed between a last firing event and the next firingevent.

During the combustion stroke, the combustion of the air/fuel mixturedrives the piston down, thereby driving the crankshaft. The combustionstroke may be defined as the time between the piston reaching TDC andthe time at which the piston returns to bottom dead center (BDC).

During the exhaust stroke, the piston begins moving up from BDC andexpels the byproducts of combustion through an exhaust valve 130. Thebyproducts of combustion are exhausted from the vehicle via an exhaustsystem 134.

The intake valve 122 may be controlled by an intake camshaft 140, whilethe exhaust valve 130 may be controlled by an exhaust camshaft 142. Invarious implementations, multiple intake camshafts (including the intakecamshaft 140) may control multiple intake valves (including the intakevalve 122) for the cylinder 118 and/or may control the intake valves(including the intake valve 122) of multiple banks of cylinders(including the cylinder 118). Similarly, multiple exhaust camshafts(including the exhaust camshaft 142) may control multiple exhaust valvesfor the cylinder 118 and/or may control exhaust valves (including theexhaust valve 130) for multiple banks of cylinders (including thecylinder 118).

The cylinder actuator module 120 may deactivate the cylinder 118 bydisabling opening of the intake valve 122 and/or the exhaust valve 130.In various other implementations, the intake valve 122 and/or theexhaust valve 130 may be controlled by devices other than camshafts,such as electromagnetic actuators.

The time at which the intake valve 122 is opened may be varied withrespect to piston TDC by an intake cam phaser 148. The time at which theexhaust valve 130 is opened may be varied with respect to piston TDC byan exhaust cam phaser 150. A phaser actuator module 158 may control theintake cam phaser 148 and the exhaust cam phaser 150 based on signalsfrom the ECM 114. When implemented, variable valve lift (not shown) mayalso be controlled by the phaser actuator module 158.

The engine system 100 may include a boost device that providespressurized air to the intake manifold 110. For example, FIG. 1 shows aturbocharger including a hot turbine 160-1 that is powered by hotexhaust gases flowing through the exhaust system 134. The turbochargeralso includes a cold air compressor 160-2, driven by the turbine 160 1,that compresses air leading into the throttle valve 112. In variousimplementations, a supercharger (not shown), driven by the crankshaft,may compress air from the throttle valve 112 and deliver the compressedair to the intake manifold 110.

A wastegate 162 may allow exhaust to bypass the turbine 160 1, therebyreducing the boost (the amount of intake air compression) of theturbocharger. The ECM 114 may control the turbocharger via a boostactuator module 164. The boost actuator module 164 may modulate theboost of the turbocharger by controlling the position of the wastegate162. In various implementations, multiple turbochargers may becontrolled by the boost actuator module 164. The turbocharger may havevariable geometry, which may be controlled by the boost actuator module164.

An intercooler (not shown) may dissipate some of the heat contained inthe compressed air charge, which is generated as the air is compressed.The compressed air charge may also have absorbed heat from components ofthe exhaust system 134. Although shown separated for purposes ofillustration, the turbine 160-1 and the compressor 160-2 may be attachedto each other, placing intake air in close proximity to hot exhaust.

The engine system 100 may include an exhaust gas recirculation (EGR)valve 170, which selectively redirects exhaust gas back to the intakemanifold 110. The EGR valve 170 may be located upstream of theturbocharger's turbine 160-1. The EGR valve 170 may be controlled by anEGR actuator module 172.

The engine system 100 may measure the speed of the crankshaft inrevolutions per minute (RPM) using an RPM sensor 180. The temperature ofthe engine coolant may be measured using an engine coolant temperature(ECT) sensor 182. The ECT sensor 182 may be located within the engine102 or at other locations where the coolant is circulated, such as aradiator (not shown).

The pressure within the intake manifold 110 may be measured using amanifold absolute pressure (MAP) sensor 184. In various implementations,engine vacuum, which is the difference between ambient air pressure andthe pressure within the intake manifold 110, may be measured. The massflow rate of air being drawn into the engine 102 may be measured using amass airflow (MAF) sensor 186. The pressure of air at the inlet of thethrottle valve 112 may be measured using a throttle inlet air pressure(TIAP) sensor 188.

The throttle actuator module 116 may monitor the position of thethrottle valve 112 using one or more throttle position sensors (TPS)190. The ambient temperature of air being drawn into the engine 102 maybe measured using an intake air temperature (IAT) sensor 192. In variousimplementations, the MAF sensor 186 and the IAT sensor 192 may belocated in the same housing. In addition, the MAF sensor 186 and the IATsensor 192 may be located upstream from the turbocharger's compressor160-2 to protect the sensors 186, 192 from heat generated as air iscompressed by the turbocharger's compressor 160-2. The ECM 114 may usesignals from the sensors to make control decisions for the engine system100.

The ECM 114 may communicate with a transmission control module 194 tocoordinate shifting gears in a transmission (not shown). For example,the ECM 114 may reduce engine torque during a gear shift. The ECM 114may communicate with a hybrid control module 196 to coordinate operationof the engine 102 and an electric motor 198.

The electric motor 198 may also function as a generator, and may be usedto produce electrical energy for use by vehicle electrical systemsand/or for storage in a battery. In various implementations, variousfunctions of the ECM 114, the transmission control module 194, and thehybrid control module 196 may be integrated into one or more modules.

Each system that varies an engine parameter may be referred to as anactuator that receives an actuator value. For example, the throttleactuator module 116 may be referred to as an actuator and the throttleopening area may be referred to as the actuator value. In the example ofFIG. 1, the throttle actuator module 116 achieves the throttle openingarea by adjusting an angle of the blade of the throttle valve 112.

Similarly, the spark actuator module 126 may be referred to as anactuator, while the corresponding actuator value may be the amount ofspark advance relative to cylinder TDC. Other actuators may include thecylinder actuator module 120, the fuel actuator module 124, the phaseractuator module 158, the boost actuator module 164, and the EGR actuatormodule 172. For these actuators, the actuator values may correspond tonumber of activated cylinders, fueling rate, intake and exhaust camphaser angles, boost pressure, and EGR valve opening area, respectively.The ECM 114 may control actuator values in order to cause the engine 102to generate a desired engine output torque.

Referring now to FIG. 2, a functional block diagram of an exemplaryengine control system is presented. An exemplary implementation of theECM 114 includes a driver torque module 202. The driver torque module202 may determine a driver torque request based on a driver input fromthe driver input module 104. The driver input may be based on a positionof an accelerator pedal. The driver input may also be based on cruisecontrol, which may be an adaptive cruise control system that variesvehicle speed to maintain a predetermined following distance. The drivertorque module 202 may store one or more mappings of accelerator pedalposition to desired torque, and may determine the driver torque requestbased on a selected one of the mappings.

An axle torque arbitration module 204 arbitrates between the drivertorque request from the driver torque module 202 and other axle torquerequests. Axle torque (torque at the wheels) may be produced by varioussources including an engine and/or an electric motor. Torque requestsmay include absolute torque requests as well as relative torque requestsand ramp requests. For example only, ramp requests may include a requestto ramp torque down to a minimum engine off torque or to ramp torque upfrom the minimum engine off torque. Relative torque requests may includetemporary or persistent torque reductions or increases.

Axle torque requests may include a torque reduction requested by atraction control system when positive wheel slip is detected. Positivewheel slip occurs when axle torque overcomes friction between the wheelsand the road surface, and the wheels begin to slip against the roadsurface. Axle torque requests may also include a torque increase requestto counteract negative wheel slip, where a tire of the vehicle slips inthe other direction with respect to the road surface because the axletorque is negative.

Axle torque requests may also include brake management requests andvehicle over-speed torque requests. Brake management requests may reduceaxle torque to ensure that the axle torque does not exceed the abilityof the brakes to hold the vehicle when the vehicle is stopped. Vehicleover-speed torque requests may reduce the axle torque to prevent thevehicle from exceeding a predetermined speed. Axle torque requests mayalso be generated by vehicle stability control systems.

The axle torque arbitration module 204 outputs a predicted torquerequest and an immediate torque request based on the results ofarbitrating between the received torque requests. As described below,the predicted and immediate torque requests from the axle torquearbitration module 204 may selectively be adjusted by other modules ofthe ECM 114 before being used to control actuators of the engine system100.

In general terms, the immediate torque request is the amount ofcurrently desired axle torque, while the predicted torque request is theamount of axle torque that may be needed on short notice. The ECM 114therefore controls the engine system 100 to produce an axle torque equalto the immediate torque request. However, different combinations ofactuator values may result in the same axle torque. The ECM 114 maytherefore adjust the actuator values to allow a faster transition to thepredicted torque request, while still maintaining the axle torque at theimmediate torque request.

In various implementations, the predicted torque request may be based onthe driver torque request. The immediate torque request may be less thanthe predicted torque request, such as when the driver torque request iscausing wheel slip on an icy surface. In such a case, a traction controlsystem (not shown) may request a reduction via the immediate torquerequest, and the ECM 114 reduces the torque produced by the enginesystem 100 to the immediate torque request. However, the ECM 114controls the engine system 100 so that the engine system 100 can quicklyresume producing the predicted torque request once the wheel slip stops.

In general terms, the difference between the immediate torque requestand the higher predicted torque request can be referred to as a torquereserve. The torque reserve may represent the amount of additionaltorque that the engine system 100 can begin to produce with minimaldelay. Fast engine actuators are used to increase or decrease currentaxle torque. As described in more detail below, fast engine actuatorsare defined in contrast with slow engine actuators.

In various implementations, fast engine actuators are capable of varyingaxle torque within a range, where the range is established by the slowengine actuators. In such implementations, the upper limit of the rangeis the predicted torque request, while the lower limit of the range islimited by the torque capacity of the fast actuators. For example only,fast actuators may only be able to reduce axle torque by a first amount,where the first amount is a measure of the torque capacity of the fastactuators. The first amount may vary based on engine operatingconditions set by the slow engine actuators. When the immediate torquerequest is within the range, fast engine actuators can be set to causethe axle torque to be equal to the immediate torque request. When theECM 114 requests the predicted torque request to be output, the fastengine actuators can be controlled to vary the axle torque to the top ofthe range, which is the predicted torque request.

In general terms, fast engine actuators can more quickly change the axletorque when compared to slow engine actuators. Slow actuators mayrespond more slowly to changes in their respective actuator values thanfast actuators do. For example, a slow actuator may include mechanicalcomponents that require time to move from one position to another inresponse to a change in actuator value. A slow actuator may also becharacterized by the amount of time it takes for the axle torque tobegin to change once the slow actuator begins to implement the changedactuator value. Generally, this amount of time will be longer for slowactuators than for fast actuators. In addition, even after beginning tochange, the axle torque may take longer to fully respond to a change ina slow actuator.

For example only, the ECM 114 may set actuator values for slow actuatorsto values that would enable the engine system 100 to produce thepredicted torque request if the fast actuators were set to appropriatevalues. Meanwhile, the ECM 114 may set actuator values for fastactuators to values that, given the slow actuator values, cause theengine system 100 to produce the immediate torque request instead of thepredicted torque request.

The fast actuator values therefore cause the engine system 100 toproduce the immediate torque request. When the ECM 114 decides totransition the axle torque from the immediate torque request to thepredicted torque request, the ECM 114 changes the actuator values forone or more fast actuators to values that correspond to the predictedtorque request. Because the slow actuator values have already been setbased on the predicted torque request, the engine system 100 is able toproduce the predicted torque request after only the delay imposed by thefast actuators. In other words, the longer delay that would otherwiseresult from changing axle torque using slow actuators is avoided.

For example only, when the predicted torque request is equal to thedriver torque request, a torque reserve may be created when theimmediate torque request is less than the driver torque request due to atemporary torque reduction request. Alternatively, a torque reserve maybe created by increasing the predicted torque request above the drivertorque request while maintaining the immediate torque request at thedriver torque request. The resulting torque reserve can absorb suddenincreases in required axle torque. For example only, sudden loads froman air conditioner or a power steering pump may be counterbalanced byincreasing the immediate torque request. If the increase in immediatetorque request is less than the torque reserve, the increase can bequickly produced by using fast actuators. The predicted torque requestmay then also be increased to re-establish the previous torque reserve.

Another example use of a torque reserve is to reduce fluctuations inslow actuator values. Because of their relatively slow speed, varyingslow actuator values may produce control instability. In addition, slowactuators may include mechanical parts, which may draw more power and/orwear more quickly when moved frequently. Creating a sufficient torquereserve allows changes in desired torque to be made by varying fastactuators via the immediate torque request while maintaining the valuesof the slow actuators. For example, to maintain a given idle speed, theimmediate torque request may vary within a range. If the predictedtorque request is set to a level above this range, variations in theimmediate torque request that maintain the idle speed can be made usingfast actuators without the need to adjust slow actuators.

For example only, in a spark-ignition engine, spark timing may be a fastactuator value, while throttle opening area may be a slow actuatorvalue. Spark-ignition engines may combust fuels including, for example,gasoline and ethanol, by applying a spark. By contrast, in acompression-ignition engine, fuel flow may be a fast actuator value,while throttle opening area may be used as an actuator value for enginecharacteristics other than torque. Compression-ignition engines maycombust fuels including, for example, diesel, by compressing the fuels.

When the engine 102 is a spark-ignition engine, the spark actuatormodule 126 may be a fast actuator and the throttle actuator module 116may be a slow actuator. After receiving a new actuator value, the sparkactuator module 126 may be able to change spark timing for the followingfiring event. When the spark timing (also called spark advance) for afiring event is set to a calibrated value, maximum torque is produced inthe combustion stroke immediately following the firing event. However, aspark advance deviating from the calibrated value may reduce the amountof torque produced in the combustion stroke. Therefore, the sparkactuator module 126 may be able to vary engine output torque as soon asthe next firing event occurs by varying spark advance. For example only,a table of spark advances corresponding to different engine operatingconditions may be determined during a calibration phase of vehicledesign, and the calibrated value is selected from the table based oncurrent engine operating conditions.

By contrast, changes in throttle opening area take longer to affectengine output torque. The throttle actuator module 116 changes thethrottle opening area by adjusting the angle of the blade of thethrottle valve 112. Therefore, once a new actuator value is received,there is a mechanical delay as the throttle valve 112 moves from itsprevious position to a new position based on the new actuator value. Inaddition, airflow changes based on the throttle valve opening aresubject to air transport delays in the intake manifold 110. Further,increased airflow in the intake manifold 110 is not realized as anincrease in engine output torque until the cylinder 118 receivesadditional air in the next intake stroke, compresses the additional air,and commences the combustion stroke.

Using these actuators as an example, a torque reserve can be created bysetting the throttle opening area to a value that would allow the engine102 to produce a predicted torque request. Meanwhile, the spark timingcan be set based on an immediate torque request that is less than thepredicted torque request. Although the throttle opening area generatesenough airflow for the engine 102 to produce the predicted torquerequest, the spark timing is retarded (which reduces torque) based onthe immediate torque request. The engine output torque will therefore beequal to the immediate torque request.

When additional torque is needed, such as when the air conditioningcompressor is started, or when traction control determines wheel sliphas ended, the spark timing can be set based on the predicted torquerequest. By the following firing event, the spark actuator module 126may return the spark advance to a calibrated value, which allows theengine 102 to produce the full engine output torque achievable with theairflow already present. The engine output torque may therefore bequickly increased to the predicted torque request without experiencingdelays from changing the throttle opening area.

When the engine 102 is a compression-ignition engine, the fuel actuatormodule 124 may be a fast actuator and the throttle actuator module 116and the boost actuator module 164 may be emissions actuators. In thismanner, the fuel mass may be set based on the immediate torque request,and the throttle opening area and boost may be set based on thepredicted torque request. The throttle opening area may generate moreairflow than necessary to satisfy the predicted torque request. In turn,the airflow generated may be more than required for complete combustionof the injected fuel such that the air/fuel ratio is usually lean andchanges in airflow do not affect the engine torque output. The engineoutput torque will therefore be equal to the immediate torque requestand may be increased or decreased by adjusting the fuel flow.

The throttle actuator module 116, the boost actuator module 164, and theEGR actuator module 172 may be controlled based on the predicted torquerequest to control emissions and to minimize turbo lag. The throttleactuator module 116 may create a vacuum to draw exhaust gases throughthe EGR valve 170 and into the intake manifold 110.

The axle torque arbitration module 204 may output the predicted torquerequest and the immediate torque request to a propulsion torquearbitration module 206. In various implementations, the axle torquearbitration module 204 may output the predicted and immediate torquerequests to a hybrid optimization module 208. The hybrid optimizationmodule 208 determines how much torque should be produced by the engine102 and how much torque should be produced by the electric motor 198.The hybrid optimization module 208 then outputs modified predicted andimmediate torque requests to the propulsion torque arbitration module206. In various implementations, the hybrid optimization module 208 maybe implemented in the hybrid control module 196.

The predicted and immediate torque requests received by the propulsiontorque arbitration module 206 are converted from an axle torque domain(torque at the wheels) into a propulsion torque domain (torque at thecrankshaft). This conversion may occur before, after, as part of, or inplace of the hybrid optimization module 208.

The propulsion torque arbitration module 206 arbitrates betweenpropulsion torque requests, including the converted predicted andimmediate torque requests. The propulsion torque arbitration module 206generates an arbitrated predicted torque request and an arbitratedimmediate torque request. The arbitrated torques may be generated byselecting a winning request from among received requests. Alternativelyor additionally, the arbitrated torques may be generated by modifyingone of the received requests based on another one or more of thereceived requests.

Other propulsion torque requests may include torque reductions forengine over-speed protection, torque increases for stall prevention, andtorque reductions requested by the transmission control module 194 toaccommodate gear shifts. Propulsion torque requests may also result fromclutch fuel cutoff, which reduces the engine output torque when thedriver depresses the clutch pedal in a manual transmission vehicle toprevent a flare (rapid rise) in engine speed.

Propulsion torque requests may also include an engine shutoff request,which may be initiated when a critical fault is detected. For exampleonly, critical faults may include detection of vehicle theft, a stuckstarter motor, electronic throttle control problems, and unexpectedtorque increases. In various implementations, when an engine shutoffrequest is present, arbitration selects the engine shutoff request asthe winning request. When the engine shutoff request is present, thepropulsion torque arbitration module 206 may output zero as thearbitrated torques.

In various implementations, an engine shutoff request may simply shutdown the engine 102 separately from the arbitration process. Thepropulsion torque arbitration module 206 may still receive the engineshutoff request so that, for example, appropriate data can be fed backto other torque requestors. For example, all other torque requestors maybe informed that they have lost arbitration.

An RPM control module 210 may also output predicted and immediate torquerequests to the propulsion torque arbitration module 206. The torquerequests from the RPM control module 210 may prevail in arbitration whenthe ECM 114 is in an RPM mode. RPM mode may be selected when the driverremoves their foot from the accelerator pedal, such as when the vehicleis idling or coasting down from a higher speed. Alternatively oradditionally, RPM mode may be selected when the predicted torque requestfrom the axle torque arbitration module 204 is less than a predeterminedtorque value.

The RPM control module 210 receives a desired RPM from an RPM trajectorymodule 212, and controls the predicted and immediate torque requests toreduce the difference between the desired RPM and the current RPM. Forexample only, the RPM trajectory module 212 may output a linearlydecreasing desired RPM for vehicle coastdown until an idle RPM isreached. The RPM trajectory module 212 may then continue outputting theidle RPM as the desired RPM.

A reserves/loads module 220 receives the arbitrated predicted andimmediate torque requests from the propulsion torque arbitration module206. The reserves/loads module 220 may adjust the arbitrated predictedand immediate torque requests to create a torque reserve and/or tocompensate for one or more loads. The reserves/loads module 220 thenoutputs the adjusted predicted and immediate torque requests to anactuation module 224.

For example only, a catalyst light-off process or a cold start emissionsreduction process may require retarded spark advance. The reserves/loadsmodule 220 may therefore increase the adjusted predicted torque requestabove the adjusted immediate torque request to create retarded spark forthe cold start emissions reduction process. In another example, theair/fuel ratio of the engine and/or the mass airflow may be directlyvaried, such as by diagnostic intrusive equivalence ratio testing and/ornew engine purging. Before beginning these processes, a torque reservemay be created or increased to quickly offset decreases in engine outputtorque that result from leaning the air/fuel mixture during theseprocesses.

The reserves/loads module 220 may also create or increase a torquereserve in anticipation of a future load, such as power steering pumpoperation or engagement of an air conditioning (A/C) compressor clutch.The reserve for engagement of the A/C compressor clutch may be createdwhen the driver first requests air conditioning. The reserves/loadsmodule 220 may increase the adjusted predicted torque request whileleaving the adjusted immediate torque request unchanged to produce thetorque reserve. Then, when the A/C compressor clutch engages, thereserves/loads module 220 may increase the immediate torque request bythe estimated load of the A/C compressor clutch.

The actuation module 224 receives the adjusted predicted and immediatetorque requests from the reserves/loads module 220. The actuation module224 determines how the adjusted predicted and immediate torque requestswill be achieved. The actuation module 224 may be engine type specific.For example, the actuation module 224 may be implemented differently oruse different control schemes for spark-ignition engines versuscompression-ignition engines.

In various implementations, the actuation module 224 may define aboundary between modules that are common across all engine types andmodules that are engine type specific. For example, engine types mayinclude spark-ignition and compression-ignition. Modules prior to theactuation module 224, such as the propulsion torque arbitration module206, may be common across engine types, while the actuation module 224and subsequent modules may be engine type specific.

For example, in a spark-ignition engine, the actuation module 224 mayvary the opening of the throttle valve 112 as a slow actuator thatallows for a wide range of torque control. The actuation module 224 maydisable cylinders using the cylinder actuator module 120, which alsoprovides for a wide range of torque control, but may also be slow andmay involve drivability and emissions concerns. The actuation module 224may use spark timing as a fast actuator. However, spark timing may notprovide as much range of torque control. In addition, the amount oftorque control possible with changes in spark timing (referred to asspark reserve capacity) may vary as airflow changes.

In various implementations, the actuation module 224 may generate an airtorque request based on the adjusted predicted torque request. The airtorque request may be equal to the adjusted predicted torque request,setting airflow so that the adjusted predicted torque request can beachieved by changes to other actuators.

An air control module 228 may determine desired actuator values based onthe air torque request. For example, the air control module 228 maycontrol desired manifold absolute pressure (MAP), desired throttleintake air pressure (TIAP), desired throttle area, and/or desired airper cylinder (APC). Desired MAP and desired TIAP may be used todetermine desired boost, and desired APC may be used to determinedesired cam phaser positions. In various implementations, the aircontrol module 228 may also determine an amount of opening of the EGRvalve 170.

The actuation module 224 may also generate a spark torque request, acylinder shut-off torque request, and a fuel torque request. The sparktorque request may be used by a spark control module 232 to determinehow much to retard the spark timing (which reduces engine output torque)from a calibrated spark advance.

The cylinder shut-off torque request may be used by a cylinder controlmodule 236 to determine how many cylinders to deactivate. The cylindercontrol module 236 may instruct the cylinder actuator module 120 todeactivate one or more cylinders of the engine 102. In variousimplementations, a predefined group of cylinders may be deactivatedjointly.

The cylinder control module 236 may also instruct a fuel control module240 to stop providing fuel for deactivated cylinders and may instructthe spark control module 232 to stop providing spark for deactivatedcylinders. In various implementations, the spark control module 232 onlystops providing spark for a cylinder once any fuel/air mixture alreadypresent in the cylinder has been combusted.

In various implementations, the cylinder actuator module 120 may includea hydraulic system that selectively decouples intake and/or exhaustvalves from the corresponding camshafts for one or more cylinders inorder to deactivate those cylinders. For example only, valves for halfof the cylinders are either hydraulically coupled or decoupled as agroup by the cylinder actuator module 120. In various implementations,cylinders may be deactivated simply by halting provision of fuel tothose cylinders, without stopping the opening and closing of the intakeand exhaust valves. In such implementations, the cylinder actuatormodule 120 may be omitted.

The fuel control module 240 may vary the amount of fuel provided to eachcylinder based on the fuel torque request from the actuation module 224.During normal operation of a spark-ignition engine, the fuel controlmodule 240 may operate in an air lead mode in which the fuel controlmodule 240 attempts to maintain a stoichiometric air/fuel ratio bycontrolling fuel flow based on airflow. The fuel control module 240 maydetermine a fuel mass that will yield stoichiometric combustion whencombined with the current amount of air per cylinder. The fuel controlmodule 240 may instruct the fuel actuator module 124 via the fuelingrate to inject this fuel mass for each activated cylinder.

In compression-ignition systems, the fuel control module 240 may operatein a fuel lead mode in which the fuel control module 240 determines afuel mass for each cylinder that satisfies the fuel torque request whileminimizing emissions, noise, and fuel consumption. In the fuel leadmode, airflow is controlled based on fuel flow and may be controlled toyield a lean air/fuel ratio. In addition, the air/fuel ratio may bemaintained above a predetermined level, which may prevent black smokeproduction in dynamic engine operating conditions.

A mode setting may determine how the actuation module 224 treats theadjusted immediate torque request. The mode setting may be provided tothe actuation module 224, such as by the propulsion torque arbitrationmodule 206, and may select modes including an inactive mode, a pleasiblemode, a maximum range mode, and an auto actuation mode.

In the inactive mode, the actuation module 224 may ignore the adjustedimmediate torque request and set engine output torque based on theadjusted predicted torque request. The actuation module 224 maytherefore set the spark torque request, the cylinder shut-off torquerequest, and the fuel torque request to the adjusted predicted torquerequest, which maximizes engine output torque for the current engineairflow conditions. Alternatively, the actuation module 224 may setthese requests to predetermined (such as out-of-range high) values todisable torque reductions from retarding spark, deactivating cylinders,or reducing the fuel/air ratio.

In the pleasible mode, the actuation module 224 outputs the adjustedpredicted torque request as the air torque request and attempts toachieve the adjusted immediate torque request by adjusting only sparkadvance. The actuation module 224 therefore outputs the adjustedimmediate torque request as the spark torque request. The spark controlmodule 232 will retard the spark as much as possible to attempt toachieve the spark torque request. If the desired torque reduction isgreater than the spark reserve capacity (the amount of torque reductionachievable by spark retard), the torque reduction may not be achieved.The engine output torque will then be greater than the adjustedimmediate torque request.

In the maximum range mode, the actuation module 224 may output theadjusted predicted torque request as the air torque request and theadjusted immediate torque request as the spark torque request. Inaddition, the actuation module 224 may decrease the cylinder shut-offtorque request (thereby deactivating cylinders) when reducing sparkadvance alone is unable to achieve the adjusted immediate torquerequest.

In the auto actuation mode, the actuation module 224 may decrease theair torque request based on the adjusted immediate torque request. Invarious implementations, the air torque request may be reduced only sofar as is necessary to allow the spark control module 232 to achieve theadjusted immediate torque request by adjusting spark advance. Therefore,in auto actuation mode, the adjusted immediate torque request isachieved while adjusting the air torque request as little as possible.In other words, the use of relatively slowly-responding throttle valveopening is minimized by reducing the quickly-responding spark advance asmuch as possible. This allows the engine 102 to return to producing theadjusted predicted torque request as quickly as possible.

A torque estimation module 244 may estimate torque output of the engine102. This estimated torque may be used by the air control module 228 toperform closed-loop control of engine airflow parameters, such asthrottle area, MAP, and phaser positions. For example, a torquerelationship such asT=f(APC,S,I,E,AF,OT,#)  (1)may be defined, where torque (T) is a function of air per cylinder(APC), spark advance (S), intake cam phaser position (I), exhaust camphaser position (E), air/fuel ratio (AF), oil temperature (OT), andnumber of activated cylinders (#). Additional variables may also beaccounted for, such as the degree of opening of an exhaust gasrecirculation (EGR) valve.

This relationship may be modeled by an equation and/or may be stored asa lookup table. The torque estimation module 244 may determine APC basedon measured MAF and current RPM, thereby allowing closed loop aircontrol based on actual airflow. The intake and exhaust cam phaserpositions used may be based on actual positions, as the phasers may betraveling toward desired positions.

The actual spark advance may be used to estimate the actual engineoutput torque. When a calibrated spark advance value is used to estimatetorque, the estimated torque may be called an estimated air torque, orsimply air torque. The air torque is an estimate of how much torque theengine could generate at the current airflow if spark retard was removed(i.e., spark timing was set to the calibrated spark advance value) andall cylinders were fueled.

The air control module 228 may output a desired area signal to thethrottle actuator module 116. The throttle actuator module 116 thenregulates the throttle valve 112 to produce the desired throttle area.The air control module 228 may generate the desired area signal based onan inverse torque model and the air torque request. The air controlmodule 228 may use the estimated air torque and/or the MAF signal inorder to perform closed loop control. For example, the desired areasignal may be controlled to minimize a difference between the estimatedair torque and the air torque request.

The air control module 228 may output a desired manifold absolutepressure (MAP) signal to a boost control module 248. The boost controlmodule 248 determines a desired boost pressure based on the desired MAPsignal and outputs a desired boost pressure signal to control the boostactuator module 164. The boost actuator module 164 then controls one ormore turbochargers (e.g., the turbocharger including the turbine 160-1and the compressor 160-2) and/or superchargers.

The air control module 228 may also output a desired air per cylinder(APC) signal to a phaser scheduling module 252. Based on the desired APCsignal and the RPM signal, the phaser scheduling module 252 may controlpositions of the intake and/or exhaust cam phasers 148 and 150 using thephaser actuator module 158.

Referring back to the spark control module 232, calibrated spark advancevalues may vary based on various engine operating conditions. Forexample only, a torque relationship may be inverted to solve for desiredspark advance. For a given torque request (Tdes), the desired sparkadvance (Sdes) may be determined based onS _(des) =f ⁻¹(T _(des),APC,I,E,AF,OT,#).  (2)This relationship may be embodied as an equation and/or as a lookuptable. The air/fuel ratio (AF) may be the actual air/fuel ratio, asreported by the fuel control module 240.

When the spark advance is set to the calibrated spark advance, theresulting torque may be as close to mean best torque (MBT) as possible.MBT refers to the maximum engine output torque that is generated for agiven airflow as spark advance is increased, while using fuel having anoctane rating greater than a predetermined threshold and usingstoichiometric fueling. The spark advance at which this maximum torqueoccurs is referred to as MBT spark. The calibrated spark advance maydiffer slightly from MBT spark because of, for example, fuel quality(such as when lower octane fuel is used) and environmental factors. Thetorque at the calibrated spark advance may therefore be less than MBT.

Referring now to FIG. 3, the air control module 228 may include variousmodules that determine the desired MAP and the desired throttle areabased on the air torque request. A torque adjustment module 302 performsclosed loop control by adjusting the air torque request to minimize adifference between the air torque request and the estimated air torque.The torque adjustment module 302 outputs the adjusted air torque.

The MAP determination module 304 may determine the desired MAP based onthe inverse torque model and the adjusted air torque. Additionally, theMAP determination module 304 may determine the desired MAP based on theinverse torque model and the air torque request. The MAP determinationmodule 304 may perform closed loop control by adjusting the desired MAPto minimize a difference between the desired MAP and an actual MAPmeasured by the MAP sensor 184. The MAP determination module 304 outputsthe desired MAP.

The APC determination module 306 may determine the desired APC based onthe inverse torque model and the adjusted air torque. Additionally, theAPC determination module 306 may determine the desired APC based on theinverse torque model and the air torque request. The APC determinationmodule 306 may perform closed loop control by adjusting the desired APCto minimize a difference between the desired APC and an actual APC. Theactual APC may be determined based on the mass flow rate measured by theMAF sensor 186 and the number of activated cylinders. The APCdetermination module 306 outputs the desired APC.

A basic boost module 308 determines a basic boost pressure based onatmospheric pressure and design parameters of the boost device. Thebasic boost module 308 may assume the atmospheric pressure is equal tostandard atmospheric pressure (100 kPa) and/or determine the atmosphericpressure based on output from a pressure sensor (not shown). The designparameters of the boost device may include the size of the wastegate,the area of a diaphragm on which compressed air acts to urge thewastegate open, and the rate of a spring acting on the diaphragm to urgethe wastegate closed. The design parameters of the boost device may bepredetermined.

A boost offset module 310 determines a boost offset pressure based onthe desired MAP and the basic boost pressure. The boost offset module310 may determine the boost offset pressure based on a predeterminedrelationship between the desired MAP, the basic boost pressure, and theboost offset pressure. This predetermined relationship may be embodiedas an equation and/or as a lookup table. The boost offset pressure maybe greater than zero when the desired MAP is less than a first pressure.The first pressure may be greater than the basic boost pressure and maybe predetermined to correspond to a duty cycle of the wastegate. Forexample, the first pressure may be approximately 10 kPa greater than thebasic boost pressure.

The boost offset module 310 may add the boost offset pressure to thedesired MAP to obtain a desired TIAP and output the desired TIAP. Theboost control module 248 may then determine the desired boost pressurebased on the desired TIAP. Alternatively, the boost offset module 310may output the desired MAP and the boost offset pressure. The boostcontrol module 248 may then add the boost offset pressure to the desiredMAP to obtain the desired TIAP and determine the desired boost pressurebased on the desired TIAP. Either way, the boost control module 248determines the desired boost pressure based on a sum of the desired MAPand the boost offset pressure.

A throttle offset module 312 determines a throttle offset pressure basedon the desired MAP and the basic boost pressure. The throttle offsetmodule 312 may determine the throttle offset pressure based on apredetermined relationship between the desired MAP, the basic boostpressure, and the throttle offset pressure. This predeterminedrelationship may be embodied as an equation and/or as a lookup table.The throttle offset pressure may be greater than zero when the desiredMAP is greater than the first pressure. The throttle offset module 312outputs the throttle offset pressure.

A throttle control module 314 determines the desired throttle area basedon a product of a desired airflow and a desired flow density. Thethrottle control module 314 may determine the desired airflow based onthe desired APC, the number of activated cylinders, and the current RPM(or engine speed). The throttle control module 314 may determine thedesired flow density based on a relationship such as

$\begin{matrix}{{{F\; D} = \frac{\left( {R*I\; A\; T} \right)^{1/2}}{\psi*T\; I\; A\; P}},} & (3)\end{matrix}$where the desired flow density (FD) is a function of the gas constant(R), the intake air temperature (IAT), the compressible flow function(ψ), and the throttle inlet air pressure (TIAP). This relationship maybe embodied as an equation and/or as a lookup table. The compressibleflow function is a function of the desired MAP and the TIAP.

The throttle control module 314 may add the throttle offset pressure tothe desired MAP before determining the desired flow density based on thedesired MAP. The throttle control module 314 may determine the throttleinlet air pressure, the throttle angle, and the intake air temperatureand based on input received from the TIAP sensor 188, the TPS sensor190, and the IAT sensor 192, respectively. The gas constant is 8.31Joules per mole-Kelvin (J/mol-K). The throttle control module 314outputs the desired throttle area.

Referring now to FIG. 4, an engine control method according to thepresent disclosure begins at 402. At 404, the method determines adesired MAP. The method may determine the desired MAP based on a drivertorque request and engine operating conditions. The engine operatingconditions may include an actual MAP.

At 406, the method determines a desired APC. The method may determinethe desired APC based on a driver torque request and engine operatingconditions. The engine operating conditions may include a mass flow ratethrough an intake valve.

At 408, the method determines a basic boost pressure. A wastegate of aboost device may be actuated using boost pressure, and the boostpressure may be insufficient to actuate the wastegate when the boostpressure is less than the basic boost pressure. The method may determinethe basic boost pressure based on atmospheric pressure and designparameters of the boost device.

At 410, the method determines a boost offset pressure. The method maydetermine the boost offset pressure based on the desired MAP and thebasic boost pressure. The boost offset pressure may be greater than zerowhen the desired MAP is less than a first pressure. The first pressuremay be greater than the basic boost pressure and may be predetermined tocorrespond to a duty cycle of the wastegate. For example, the firstpressure may be approximately 10 kPa greater than the basic boostpressure.

At 412, the method determines a desired boost pressure. The method maydetermine the desired boost pressure based on a sum of the desired MAPand the boost offset pressure. The method may control the boost devicebased on the desired boost pressure.

At 414, the method determines a throttle offset pressure. The method maydetermine the throttle offset pressure based on the desired MAP and thebasic boost pressure. The throttle offset pressure may be greater thanzero when the desired MAP is less than the first pressure.

At 416, the method determines a desired throttle area. The method maydetermine the desired throttle area based on the sum of the desired MAPand the throttle offset pressure. The method may control a throttlevalve based on the desired throttle area. The method ends at 418.

Referring now to FIG. 5, an x-axis 502 represents torque requests inNewton-meters (N-m) and a y-axis 504 represents pressure in kilopascals(kPa). A first desired MAP 506 is determined based on the torquerequest. A desired TIAP 508 is a sum of the first desired MAP 506 and aboost offset pressure 512. A second desired MAP 510 is a sum of thefirst desired MAP 506 and a throttle pressure offset 514.

A throttle valve and a boost device may be controlled based on the firstdesired MAP 506. The response gain of the boost device is mostconsistent when a duty cycle of the wastegate is greater than a firstpercent (e.g., 30 percent). The duty cycle of the wastegate is equal tothe first percent when the first desired MAP 506 is equal to a firstpressure 516. The first pressure 516 is equal to a sum of a basic boostpressure 518 and approximately 10 kPa. The basic boost pressure 518 is aminimum boost pressure (e.g., 145 kPa) sufficient to actuate a wastegateof the boost device.

The response gain of the throttle valve is most consistent when adesired pressure ratio across the throttle valve is less than a firstratio (e.g., 0.9). The desired pressure ratio across the throttle valveis a ratio of a desired pressure downstream from the throttle valve(i.e., a desired MAP) to the pressure upstream from the throttle valve.The pressure upstream from the throttle valve is equal to atmosphericpressure 520 when the boost device is incapable of developing boostpressure.

The desired pressure ratio is equal to the first ratio when the firstdesired MAP 506 is equal to a second pressure 522. The second pressure522 is equal to a product of the first ratio and the atmosphericpressure 520. For example, the second pressure 522 may be equal to 90kPa when the first ratio is 0.9 and the atmospheric pressure 520 isequal to standard atmospheric pressure (100 kPa).

Actuation of the throttle valve and the boost device may be coordinatedby using the throttle valve and the boost device as a primary actuatorin the desired MAP ranges corresponding to when the response gain of theactuators are most consistent. The throttle valve may be used as theprimary actuator when the first desired MAP 506 is less than the firstpressure 516. The boost device may be used as the primary actuator whenthe first desired MAP 506 is greater than the first pressure 516.

The throttle valve may be used as the primary actuator by controllingthe boost device based on the desired TIAP 508. The boost offsetpressure 512 may be predetermined to ensure that the wastegate of theboost device is fully closed when the boost device is controlled basedon the desired TIAP 508. This builds boost at a faster rate duringacceleration and causes the response gain of the boost device to beconsistent earlier in the acceleration (i.e., at a lower torquerequest). In turn, the ability to control intake airflow and enginetorque is improved when the first desired MAP 506 is between the secondpressure 522 and the first pressure 516.

The boost device may be used as the primary actuator by controlling thethrottle valve based on the second desired MAP 510. The throttle offsetpressure 514 may be predetermined to ensure that the throttle valve isfully opened when the boost device is controlled based on the firstdesired MAP 506. However, the throttle valve may be closed when theboost device overshoots the first desired MAP 506 by more than thethrottle offset pressure 514 and reopened when the boost device regainscontrol.

Referring now to FIG. 6, an x-axis 602 represents a duty cycle of awastegate in percentage and a y-axis 604 represents pressure in kPa. Aresponse gain of a boost device is represented by change in the dutycycle versus change in a boost pressure 606. As indicated above, theresponse gain of a boost device is most consistent when the duty cycleis greater than 30 percent. The response gain of the boost device isrelatively low when the duty cycle is less than 30 percent.

Referring now to FIG. 7, an x-axis 702 represents a pressure ratioacross a throttle valve and a y-axis 704 represents the compressibleflow function discussed above with reference to FIG. 3. A response gainof the throttle valve is represented by change in the compressible flowfunction versus change in a pressure ratio 706. As indicated above, theresponse gain of the throttle valve is most consistent when the pressureratio 706 is less than 0.9. The response gain of the throttle valve isrelatively high when the pressure ratio 706 is greater than 0.9.

The broad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent to the skilled practitioner upon astudy of the drawings, the specification, and the following claims.

What is claimed is:
 1. A system, comprising: a manifold air pressure(MAP) determination module that determines a desired MAP based on adriver torque request; a boost control module that controls a wastegateof a boost device based on the desired MAP; and a throttle controlmodule that controls a throttle valve based on the desired MAP, wherein:the boost control module fully closes the wastegate of the boost devicewhen the desired MAP is less than a first pressure; and the throttlecontrol module fully opens the throttle valve when the desired MAP isgreater than the first pressure.
 2. The system of claim 1, furthercomprising a basic boost module that determines a basic boost pressurebased on atmospheric pressure, wherein: the boost control modulecontrols the wastegate of the boost device based on the basic boostpressure; the throttle control module controls the throttle valve basedon the basic boost pressure; and the wastegate of the boost device isactuated using boost pressure and the boost pressure is insufficient toactuate the wastegate of the boost device when the boost pressure isless than the basic boost pressure.
 3. The system of claim 2, furthercomprising a boost offset module that determines a boost offset pressurebased on the desired MAP and the basic boost pressure, wherein the boostcontrol module controls the boost device based on the boost offsetpressure.
 4. The system of claim 3, wherein the boost control moduledetermines a desired boost pressure based on a sum of the desired MAPand the boost offset pressure, and the boost control module controls theboost device based on the desired boost pressure.
 5. The system of claim4, wherein the boost offset pressure is predetermined to cause thewastegate of the boost device to fully close when the desired MAP isless than the first pressure.
 6. The system of claim 5, furthercomprising a throttle offset module that determines a throttle offsetpressure based on the desired MAP and the basic boost pressure, whereinthe throttle control module controls the throttle valve based on thethrottle offset pressure.
 7. The system of claim 6, wherein the throttlecontrol module determines a desired throttle area based on a sum of thedesired MAP and the throttle offset pressure, and the throttle controlmodule controls the throttle valve based on the desired throttle area.8. The system of claim 7, further comprising an air per cylinder (APC)determination module that determines a desired APC based on the drivertorque request, wherein the throttle control module determines thedesired throttle area based on the desired APC.
 9. The system of claim7, wherein the throttle offset pressure is predetermined to cause thethrottle valve to fully open when the desired MAP is greater than thefirst pressure.
 10. The system of claim 9, wherein the first pressure isgreater than the basic boost pressure by a predetermined amount.
 11. Amethod, comprising: determining a desired manifold air pressure (MAP)based on a driver torque request; controlling a wastegate of a boostdevice based on the desired MAP; controlling a throttle valve based onthe desired MAP; fully closing the wastegate of the boost device whenthe desired MAP is less than a first pressure; and fully opening thethrottle valve when the desired MAP is greater than the first pressure.12. The method of claim 11, further comprising: determining a basicboost pressure based on atmospheric pressure controlling the wastegateof the boost device based on the basic boost pressure; and controllingthe throttle valve based on the basic boost pressure, wherein thewastegate of the boost device is actuated using boost pressure and theboost pressure is insufficient to actuate the wastegate of the boostdevice when the boost pressure is less than the basic boost pressure.13. The method of claim 12, further comprising: determining a boostoffset pressure based on the desired MAP and the basic boost pressure;and controlling the boost device based on the boost offset pressure. 14.The method of claim 13, further comprising: determining a desired boostpressure based on a sum of the desired MAP and the boost offsetpressure; and controlling the boost device based on the desired boostpressure.
 15. The method of claim 14, wherein the boost offset pressureis predetermined to cause the wastegate of the boost device to fullyclose when the desired MAP is less than the first pressure.
 16. Themethod of claim 15, further comprising: determining a throttle offsetpressure based on the desired MAP and the basic boost pressure; andcontrolling the throttle valve based on the throttle offset pressure.17. The method of claim 16, further comprising: determining a desiredthrottle area based on a sum of the desired MAP and the throttle offsetpressure; and controlling the throttle valve based on the desiredthrottle area.
 18. The method of claim 17, further comprising:determining a desired air per cylinder (APC) based on the driver torquerequest; and determining the desired throttle area based on the desiredAPC.
 19. The method of claim 17, wherein the throttle offset pressure ispredetermined to cause the throttle valve to fully open when the desiredMAP is greater than the first pressure.
 20. The method of claim 19,wherein the first pressure is greater than the basic boost pressure by apredetermined amount.